This invention relates to a screw joint tightening power tool with a torque limiting means. In particular the invention concerns a power tool comprising a housing, a rotation rotor mounted in said housing, an output spindle connectable to a screw joint engaging means, at least one planetary reduction gear including a ring rear which is rotatively supported in said housing, and a torque responsive release clutch associated with said planetary gear and arranged to maximize the output torque delivered by said output spindle.
A power tool of the above type is previously described in U.S. Pat. No. 3,834,467. This known tool is rather complicated in construction since it incorporates two cam following rollers which are journalled on the ring gear of the planetary gearing as well as an axially displaceable cam member which is coupled to a motor shut off means in the form of a bellows operated air supply valve. Since the two cam following rollers are journalled on the ring gear and rotate with the latter, the angular distance during which the motor and other rotating parts of the tool are to be stopped at motor shut off cannot exceed half a revolution. Often that is too short a distance to avoid a further overriding of the cams and causing of a torque adding impulse in the output spindle.
The invention intends to solve the above problems by incorporating into the power tool the characterizing features stated in the claims.